1. Field of the Invention
This invention relates generally to throttles for controlling flow through intake systems of internal combustion engines, and more specifically to a throttle body module having improved sealing of a throttle blade to the throttle body wall when in closed position.
2. Background Information, Including Reference To A Related Patent Application And Incorporation By Reference
Spark-ignited, fuel-injected internal combustion engines enjoy extensive usage as the powerplants of automotive vehicles. A representative intake system for such an engine comprises a throttle body that has a through-bore within which a throttle blade, or throttle plate, also sometimes referred to as a butterfly, is disposed. The throttle blade is fastened to a cylindrical shaft whose axis is substantially coincident with a diameter of the through-bore. The shaft is journaled on opposite wall portions of the throttle body for motion about its own axis. An actuator that is external to the through-bore selectively positions the shaft about its own axis, to thereby selectively position the throttle blade within the through-bore over a range of positions spanning a closed throttle position and a full open throttle position.
Various throttle bodies are documented in patent, and other, literature. Commonly owned, U.S. Pat. No. 5,979,871 discloses a Clamshell Throttle Body Assembly. That throttle body comprises two body halves that meet face-to-face at a common mating plane that is perpendicular to a central longitudinal axis of the throttle body that coincides with that of a central circular through-bore of the throttle body. The two body halves possess respective confronting faces at the common mating plane, and those faces circumscribe the circular through-bore through which filtered air is conveyed toward combustion chambers of the engine when the throttle body is in use on an engine. Formed in each face of the respective throttle body halves in adjoining relation to the through-bore at each of opposite ends of a diameter of the throttle body that lies in the common mating plane, is one half of a respective circular aperture centered substantially on that diameter. The two faces thereby cooperatively form the two circular apertures, each diametrically opposite the other across the through-bore. Before the two body halves are assembled together, a throttle mechanism comprising a circular throttle blade of uniform thickness disposed on a throttle shaft is placed between the two faces for subsequent capture. As the throttle body halves are moved relative to one another to place their mutually confronting faces on the common mating plane, portions of the shaft that are beyond the perimeter of the throttle blade at each end of the diameter that is coincident with the shaft axis become captured between two confronting halves of each circular aperture at corresponding ends of the diameter. A respective circular annular bearing assembly is disposed on each respective portion of the shaft that is beyond the throttle blade perimeter. Each bearing assembly has an inner circular race, an outer circular race, and a plurality of ball bearing elements, or alternatively roller elements, that are captured between the inner and outer races. In the regions where the bearing assemblies are disposed, each of the two circular apertures cooperatively defined by the throttle body halves is fashioned with confronting circular shoulders that are coaxial with the throttle shaft axis and serve to capture the respective bearing assembly, not only circumferentially, but also in the direction of the diameter of the throttle shaft.
Proximate the confronting faces of the two throttle body halves at the common mating plane, the through-bore wall comprises two generally semi-circular ledges, one in one throttle body half and the other in the other throttle body half. Each ledge is spaced from the common mating plane a distance equal to one-half the thickness of the throttle blade. One ledge occupies essentially one semi-circumference of the throttle body, and the other, essentially an opposite semi-circumference. The throttle blade mounting on the shaft is via a through-slot in the that portion of the throttle shaft which spans the throttle body through-bore. The through-slot has a thickness that is just sufficient to allow the throttle blade to pass through and that is symmetric with respect to the shaft axis. Each ledge is spaced from the common mating plane along the direction of the through-bore axis, a distance equal to essentially one-half the throttle blade thickness. When the throttle blade is in closed position it assumes an orientation that is perpendicular to the through-bore axis, with opposite semi-circular margins of its circular perimeter being disposed flat against the opposite semi-circular ledges.
While the surface-to-surface abutment of the blade perimeter to the ledges in that clam shell type throttle body provides well-defined internal sealing of a flat circular throttle blade to the through-bore when the throttle is closed, it has been discovered that a further improvement in sealing the perimeter of the blade to the ledges can be made. More especially it has been discovered that for a certain thickness of a uniformly thick throttle blade, intake manifold vacuum can impart a slight deformation to the blade when the blade is closed. The blade shape changes from one that is flat and planar throughout to one in which the blade half whose upstream facing perimeter is being forced against the ledge that faces downstream, will bulge slightly rather than remaining perfectly flat. The bulging may negatively influence the sealing effectiveness of the area over which that blade perimeter half bears against that ledge. It is believed that what may seem to be a rather small or inconsequential derogation of sealing effectiveness can in fact affect an engine's ability to comply with relevant specifications and/or regulations, especially when one recognizes that when the throttle blade is closed, a running engine creates substantial intake manifold vacuum. The opposite half of the blade whose downstream facing perimeter is being forced against the ledge that faces upstream does not appear affected in the same way.
The entire content of pending U.S. Pat. No. 5,979,871 is incorporated herein by reference as if fully disclosed herein.